The present invention relates to the field of downhole packers. More particularly, the present invention relates to a new packer for closing the space between downhole well components or between well tubing and a wellbore casing or borehole wall surface.
Downhole packers seal the annulus between well tubing and the borehole or between well tubing and casing set in the wellbore. By sealing such annulus, hydrocarbon producing zones can be isolated from other regions within a wellbore, thereby preventing migration of fluid or pressure from one zone to another.
Packers typically comprise permanent or retrievable packers. Permanent packers are installed in the wellbore with mechanical compression setting tools, with fluid pressure devices, with inflatable charges, or cement or other materials pumped into an inflatable seal element. Because of the difficulty of removing permanent packers, retrievable packers have been developed to permit the deployment and retrieval of the packer from a particular location within the wellbore.
Conventional packers typically comprise a sealing element between upper and lower retaining rings or elements. U.S. Pat. No. 4,753,444 to Jackson et al. (1988) disclosed a packer having a conventional sealing element located around the outside of a mandrel. Anti-extrusion rings and back-up rings contained the seal element ends and were compressed to radially expand the seal element outwardly into contact with the well casing. U.S. Pat. No. 4,852,649 to Young (1989) disclosed packers having multiple moving packer elements which distributed stresses across the elements as the packer elements expanded to seal the wellbore annulus. In U.S. Pat. No, 5,046,557 to Manderscheid (1991), multiple seal elements were separated with spacers around the exterior surface of a mandrel. The seal elements were hydraulically set to contact the well casing.
Other concepts have been developed for specific seal requirements. In U.S. Pat. No. 5,096,209 to Ross (1992), voids were incorporated within sealing elements to modify the performance of the seal elements in the sealing gaps between multiple tubing elements. In U.S. Pat. No. 5,195,583 to Toon et al. (1993), bentonite was placed within a packer element so that contact with water caused seal element expansion to form a low pressure annular seal.
U.S. Pat. No. 5,467,822 to Zwart (1995) disclosed a fluid pressure set pack-off tool wherein a seal element was retained with rings and annular inserts. Coaxial springs reduced distortion of the seal element and facilitated retraction of the seal element following removable of the fluid pressure. Radial bores through the seal element prevented entrained air from distorting the seal element and further permitted a higher pressure to press the seal element into sealing engagement with the well casing.
Conventional packers are limited by certain factors. It is difficult or impossible to ascertain whether a packer has been completely set, or if the packer provides an effective seal within the wellbore. This is particularly true in open hole packer applications where the borehole has washed out to create a borehole diameter greater than the drill bit diameter.
Permanent packers are typically set with a selected pump pressure. Such pressure does not reliably provide confirmation that the packer has provided an effective seal within the wellbore. Even after "permanent" packers have been initially set, the packing element can shrink as concrete or other packer setting fluids shrink or leak from the packer interior, thereby losing the sealing effectiveness. Additionally, retrievable packers can lose sealing effectiveness as temperatures cycle or fluctuate within the wellbore. High well temperatures relax many sealing materials, and the pressure set between the seal material and the well casing will deteriorate.
Another disadvantage of conventional packers is that the exterior sealing element travels on the packer exterior from the well surface to the downhole location. When the packer is run thousands of meters into the wellbore, the packing seal can abrade or completely swab off the packer sleeve. This failure may not be detected until the packer is set and the pressure containment of the isolated zone fails.
In addition, conventional packers do not readily conform to irregularities in a wellbore. To provide sufficient strength to seal large downhole fluid pressures, conventional packers are constructed as composite devices which can expand in one radial direction. Such packers do not effectively conform to elliptical or oval-shaped wellbores and do not provide an effective fluid tight seal within the wellbore.
Accordingly, a need exists for an improved packer that avoids the disadvantages of conventional packers and provides a reliable seal between different components and features downhole in a wellbore.